Process for making grease



G. C. BAILEY ETAL PROCESS FOR MAKING GREASE May 27, 1952 2 SHEETSr-SHEET1 Filed Aug. 21, 1947 ATTORNEYS M y 7, 1952 G. c. BAILEY ET AL PROCESSFOR MAKING GREASE 2 SHEETS-SHEET 2 Filed Aug. 21, 194'? on a 0n H at mmd 2 s Q g IL l lnu .6 mm N0 INVENTOR. 'G .c BAI LEY ATTORNEYS PatentedMay 27, 1952 raoosss FOR MAKINGQGREASE" Grant 0.;Bailey, Royal Oak,Mica, andWilliani B; Whitney;Bartlesvilla; Okla, assignors to ,vPhillips Petroleum Company, a corporationof;

Delaware I Application August 21, 1947, Serial N0.--769,858

9 Claims.

This invention relates, to an improved lubricant. In one of itsmorespecific aspects it relates to a lubricating grease, and to methods ofpreparing such a grease, havinga greaterconsistency and a higherresistance to bleeding when prepared by rapid cooling and severeworkingthanby methods common inthe art.

Grease making, according to the prior art, usuallyconsists of heating,in a large kettle, a mixture of saponifiable oiland an aqueoussolutionof .a metalhydroxide in the presence of a mineral oil. Duringthis heating, which requires fromB to. 24 hours, a soapis formed most ofthe water is boiled'ofi, and the soap becomes dispersed in themineraloil to form grease which is usually diluted and gradually cooledbylthe slow incorporation of more oil. During the heating and blendingprocess, the kettlecontent must be continually stirred to maintainintimate contact of the saponifiable oil and the aqueous alkali toprevent scorching and secure a uniform product. During a considerableportion of this time the mixture is a stiff pasteelike mass-the stirringof which consumes much power and requires the attention of a skilledgrease maker. This method requires large floor spaceand expensivespecialized equipment. The operation also lacks flexibility as smallbatches cannot conveniently nor cheaply be turned outin large kettlesnor production changed fromon type of grease to another in a shortperiod of time. Use. of large kettle equipment usuallymeans thata large,inventory of finished products is carried on hand.

There have been numerous continuous processes for making greasedescribed in the patent literature, but most Of the workers havebeeninterested in using the continuous process for saponifying the fattyoil and therefore use a temperature of about 200? F. to about 300 F. fora period of from 8 to 24 hours. Although the literature pertaining togreases contains many references relating to their preparation and whichreferences-usually contain directions for cooling and milling -(working)th directions which have been recorded refer to greaseswhich on cooling,or oncoming-and slig-ht-working, give a homogeneous grease-likestructure; The statements concerning cooling are often contradictoryandunsaponified fat, unsaponifiable portions of fat,-

free fatty acid, high molecular weight alcohol, wool fat, pitch, highmolecular weight amides, glycols, and the like. Theart is very carefulto teach that certain combinations of soapand oils alone are verydifficult if not impossible to secure and to maintainin stablecombination, and that stabilizing substances must be present to preventsyneresis, which in extreme cases forms an oilsoaked granular mass ofsoap; in liquidoil, The,

fact that this breakdown of the structure occurs for many combinationsof soap when heated in oil and cooled. rapidly, under thev heating andcooling conditions disclosed in 1 our procedure hereafter described, hasbeen repeatedly demonstrated by us. Previous reports of I improvementsin grease properties by rapid coolinghavebeeninexact as to what has beenmeant by rapid cooling. This has usually been stated as pouring out inpans to cool. The. depth is usually stated as about 4 inches and thecooling, medium is air at room temperature, although one referencespecifies layers having a depth between and inch at room temperature.Chill rolls and scrapers have been reported but the coolingisnot uniformnor rapid for the material considered as a whole.

One object of our invention-is to providea rapid and economic processforv producing greases of improved qualities.

Another object of our, invention isv to provide a method for. producing.an improved grease utilizing any one. of several metallsoap bases orcombinationsof such bases;

Still another object ofour invention is to,pro-;

vide a process for producing greasesof improved,

qualities by the method of extremely rapid cooling and severe working.

Afurther objectiof our. invention is to provide an improved method forproducing a grease,,- with or without an additive ,designed to impartstrength to thegel. structure, whichhas increased consistency andresistanceto bleeding,

Other objects and advantages of our invention will be apparent from theaccompanying description and discussion.-

Rapid cooling of a soap-oil mixture tends toen-v courage the formationof. granular masses in liquid oil and especially sowhen, suchoilissubstantially saturated with the soap at the elevated temperature.Aslthe initialstage in producing a superior grease, we have found thatit is-lde-h sirable to encourage by rapid cooling the formation of amass consisting of a hard; gelwhich breaks into lumps or crumbleswith orwithout the exudation of vmuch free; oil. grease-likemass is thenseverely milled (worked) to-bringit to a grease-like texturer The severemilling; process-.produces -a result which is.,.-un-

expected and contrary to that of the known art. Instead of producing agrease which continues to soften on extended working, it produces agrease which, during a process of severe working, usually increases inconsistency and always tends to reach a degree of consistency thatremains substantially constant. These greases thus produced have only aslight tendency to bleed. The reasons for these phenomena are unknownbut appear to be in the inter-relation of the metal and the fatty acidused to form the soap and in the degree of mutual solubility of the oiland soap. By rapid cooling we mean that the mixture of soap and oilshould be cooled to the desired temperature within a period of fromabout 1 to about 600 seconds, preferably between about 10 and about 300seconds.

An important application of the above described process is theproduction of a grease from a mixture comprising a stiffening agent,such as a metal soap, and oil of such a nature that the soap does notdissolve when heated in an open vessel, even when heated to atemperature just below the thermal decomposition point of theingredients, but stratifies into a lower layer of soap with a minorproportion of oil and an upper layer of oil containing a minorproportion of soap which separate phases cannot be homogenized by mildagitation. On cooling, a dense gel results from the lower layer and asoft gel from r the upper layer. On milling the two portions together, agrease of excellent quality as to the low loss of consistency isproduced, on extended working, which has only a slight tendency tobleed.

In heating the soap-oil mixture it is only necessary to heat it to apoint at which the soap begins to ball up in the oil during thestirring. That balling will usually begin to occur in the vicinity ofabout 365 F. It is not however preferred to cool from that point becausethe mixture which is formed is relatively difiicult to work. In thepreferred method of our process We continue to heat, with stirring whileadding soap to the soapoil mixture, beyond the point at which balling ofthe soap takes place and until the entire mixture is substantiallyliquefied and preferably till the oil and soap are miscible. In thismanner the oil may be substantially saturated at some temperaturebetween 365 F. and the decomposition temperature. Cooling of the mixturemay be started at or above the saturation temperature. Heating iscarried out quite rapidly so as not to injure the ingredients of themixture. The critical temperature, on heating, is that temperature atwhich thermal decomposition may occur. Precaution should be taken toavoid burning or scorching of the mixture. Our process may be utilizedin either open or closed vessels.

We have found that in many cases two greases of identical compositionwhich have been heated similarly, but one of which has been subjected tothe customary method of slow cooling and the other to the method ofrapid cooling used in our invention, show markedly differentcharacteristics. The one cooled slowly will be softer, more homogeneousand will not have as great a resistance to change of consistency onextended working nor as great a resistance to bleeding.

We have further found that this invention is not limited to theimprovement of greases of compositions now known such as a hydrocarbonoil with sodium stearate, lithium laurate, aluminum laurate, aluminumtristearate, aluminum distearate, or aluminum monostearate, but by itsapplication greases may be prepared which have hitherto not beenpossible. For example, all attempts to obtain a smooth grease by rapidcooling of solutions of anhydrous barium stearate in high viscosityindex mineral oil have failed to make a smooth stable grease whereas bythe method of rapid cooling of the heated mass to form a gel whichsynerizes, a good smooth grease was obtained by subsequent severeworking. Similar results were obtained with calcium oleate, magnesiumstearate and calcium stearate. Good results may be obtained withcombinations of these soap bases and oils but we have found that greasesmade from combinations of soap bases do not ordinarily give a productwhich is as resistant to penetration as monosoap base greases.

It has been found advantageous to substantially match the metal and thefatty acid radical so as to make the best soap and grease. Sodium soapshave been found to produce the best grease when sodium hydroxide iscombined with a fatty acid radical falling within the Cid-C20 range andpreferably with a C18 acid radical. The best lithium greases are madewhen a fatty acid radical in the Clo-C14 range and preferably a C12 acidradical is used.

The stiffening agent used in this invention is generally a soap. Such asoap is a salt of a fatty acid. The fatty acid used in making the soapshould be relatively pure. Another important factor in producing suchgreases is that the stiffening agent should generally be substantiallyneutral so that it contains substantially no free fatty acid. A greaseproduced from such a neutral stiffening agent or soap produced from arelatively pure fatty acid will, when combined with an oil as hereindescribed, form a gel which in turn will form a grease having excellentcharacteristics when it has been worked to substantially constantconsistency. By the term relatively pure fatty acid radical we mean oneof substantially the same carbon content per molecule, e. g. C18. If amixture of fatty acids is used they should be so close together instructure as to be nearly the same. Thus in making a sodium soap it isdesirable to use a fatty acid radical having 18 carbon atoms permolecule. This gives a much better grease than one prepared from a soapin which the fatty acid was a mixture of C14 to C22 fatty acids whichhad an average molecular weight equivalent to 18 carbon atoms permolecule. Fatty acid radicals differing by as much as two carbon atoms,for example C18 and C16, or C18 and C20, may be used together andproduce very satisfactory soaps, for they fall within the exceptionpointed out above in that they are bordering or adjoining structures andwill not alter the soap structure materially.

The temperature below which the grease must be cooled is that at whichsolidifying from a liquid to a gel, which is definite and possiblyrelated to the crystalline or colliodal structure of the soap, occurs.We do not, however, limit the rapid cooling to any specifiedtemperature. The limit constitutes only those conditions which willproduce a hard gel from a. solution substantially saturated under theconditions above described. This gel usually breaks or crumbles to anoil soaked mass on crushing and may be worked to a consistent grease bysevere milling or working. The temperature at which gelling of mostgreases will generally begin to take place usually falls between about330 F. and about 400 F. depending upon the type grease. The time ofcooling,

as has been pointed out above, is short, usually within a period ofbetween and 300 seconds, and the milling is equivalent to severalthousand strokes of an ASTM grease worker (Precision ScientificMotorm'atic model) as described in ASTM Test D-217-44T. By workingseverely we mean that the gel is worked an equivalent of from about2,000 to about 100,000 strokes of an ASTM grease worker. The exactnumber of strokes to be used is that number which will give the greatestconsistency to the finished grease.

In a preferred process of our invention, the soap is added tolubricating oil and heated rapidly with stirring. The soap passesthrough the stages of being merely suspended, then becoming sticky andagglomerated, then changing to a stringy, viscous mass and finallyturning to a :substantially homogeneous non-viscous liquid 01dispersion. When this stage has been reached, usually between 390 F. andabout 485 F., the mixture is cooled rapidly to form. a hard gel whichcracks, breaks, or crumbles and requires severe milling or working for ashort time to produce a smooth grease. During this milling process manygreases tend to reach a constant penetra-bility, which penetrability issubstantially maintained for several hundred thousand strokes of theASTM worker. Though we prefer that the gel formed be sufliciently hardthat it may be cracked, broken or crumbled, gels which are to somedegree softer may be severely worked with beneficial effect.

In one modification of our process, we use a soap-oil-diluent mixture,rapidly heat to a temperature between about 355 F. and about 540 F. andcool rapidly to about 285 F. As diagrammatically shown in Figure I ofthe drawing, diluent, soap and oil are delivered to mixing chamber Ithrough lines 2, 3 and 4 respectively. The materials are mixed and keptin suspension to form a substantially uniform suspension in the mixingchamber. The soap is any substantially pure fatty acid salt which issuitable for grease making. The oil is any lubricating oil suitable forgrease making and which is substantially matched with said soap. Thediluent is a low or medium boiling liquid which may or may not bemiscible with the oil. Suitable diluents would be butane or other low ormedium boiling hydrocarbon or hydrocarbon derivatives such aschlorinated hydrocarbons, ethers, esters, ketones, alcohols, alkylhalides, aldehydes, or amines. The ratio of diluent to soap-oilcombination should be such that on suddenly reduced pressure andevaporation of the diluent, the latent heat of vaporization absorbed bythe diluent shall pro duce the desired cooling eiiect described below.Mixing chamber I must be of sufficient strength to withstand the vaporpressure of the diluent at operating temperature. By metering pump 1,the mixture is forced into the heating section 8 where the mixture israpidly heated, during agitation, to a temperature between approximately355 F. and 540 F. The mixture changes on heating from a suspension ofsoap in the oildiluent mixture to substantially a liquid dispersion ofsoap in the oil-diluent mixture. This liquid is forced through anexpansion valve 9 into expansion chamber 10 which is maintained at apressure low enough to insure that substantiallyall the diluent is flashevaporated, with the result that'the soap-oil residue is cooled belowthe gelling temperature of the soap. A satisfactory temperature to whichsodium stearate may be cooled is to about 285 F. or below. Theexpansionchamber may be maintained at a'pressure above, below; or at atmosphericpressure, depending on the boiling point of the diluent used. Baflieplate l3 prevents grease from entering the exhaust with the vaporizeddiluent. The vapors are led through cooler M where they maybe cooled andcollected in condensation chamber [5. The diluent is recycled throughline IE to line 2. The residue of soap and oil is passed through greaseworker I], where it is worked severely, into storage l8, from which itis re moved by screw conveyer 2|, through filter 22 and delivered toacontainer filling machine (not shown) through line 23.

Another modified embodiment of our invention is diagrammaticallyillustrated in Figure II ,of the drawing. Lubricating oil is passedthrough line Bl into heater 62 and thence into hot oil surge tank 63.Lubricating oil is also passed from line 6| through line 64 into soapmixing. tank 65 where it is mixed with soap which is supplied throughline 68. The cold soap-in-oil slurry from soap mixing tank 65 isdischarged through line 69 into mixing tank 10 simultaneously with thedischarge of the hot oil from surge tank 63 through line 13. The hot oilis in such proportions relative to the soap-in-oil slurry that there isonly a slight drop in temperature. The soap is readily dispersed in thehot oil to form a liquid mixture. The resulting soap-in-oil dispersionis discharged continuously into cooling tank 14, which continuouslyreceives cool oil from cooler 15. The cooling tank contents are agitatedto mix quickly the hot'soap dispersion with the cool oil in the tank.The low temperature of cooling tank 14 is maintained by the inflow ofcool oil from cooler 15. The soap, on cooling below its gellingtemperature, separates as lumps of soap gel. The gel-oil mixture isdischarged to a separator 18 consisting of a centrifuge or a screensieve and the gel is separated from the oil. The free oil is recycledthrough cooler 15 to cooling tank 14 while any excess oil in the recyclesystem is returned to line 6|. The gel lumps are charged to grease mill(9 where they are mixed with the desired amount of oil from compoundingoil storage 80. It is obvious that a modification may be made in thissystem whereby a desired amount of oil may be retained with the gelpassing from separator 18 rather than adding it from storage and oilfrom another source passed through cooler 15 to cooling tank 14. Thefinished grease is discharged from grease mill 19 through line 8| tostorage or packaging machine. The hardness of the finished grease can beincreased by removing greater amounts of oil from the gel before millingwhile a softer grease may be prepared by adding greater amounts of oilbefore milling.

Three difierent oils were used in the production of the greases of ourExamples I and II. The three oils are denoted as A, B, and C. having thefollowing properties.

aawiaa (mixture comprising-80 weightper jcent mineral ,oiLA' and .20weight .per centsodium stearate were "heated tobetween .about1'392" F.and about 485 TF. One portion or "the mixture was 'then allowed to coolslowlyto room temperature'within a'i eriodfof aboutifitoiliohours..Thesecon'd portion was cooledby. fpouring'it'into a pan in which welayer was "about 5 inch thick, and the pan wa'sfthen set'in cold water.This portion cgell'ed lin about '2' minutes. 1A portion of the: slowlycooled .portion was severlyworked .or milled in ajgrease worker. as:wasthe rapidly cooled grease. These greases were then-tested with apenetrometer as described in ASTMTest 'D-21'7-44Tfbut modified so as tousea micropenetrator needle, fplung'er; "and cup, asdescribedbytKaufmangFinn and Harrington in industrial and EngineeringiChem'istry, -.analytica1 edition 115108-1110 (1939).Bleeding-tests'were' made as describedwith Armystrokes. The :unworkedpenetration of the =ra idly cooled grease was "not of significan'ceas'the productwas-a:non-homogeneous mixture-of soap and :oil. Thus,'thro'ugh the "working *ran'ge' of 10,000 to 100,000 strokes, therapidly 'cooled grease "had :ma'intaineda *more satisfactory consistency:than the'.slowlyrccoled grease.

Example .IH

such tests are "recorded -in Table'IV.

Table IV Soap - Penotmtion a[ter'90,000 Additional 1 Strokes SoapContent WVeight per eanti M illing Strokes :Penetro- Coolixi a lion Ratej (A) a (C) Y'Nae'stearate .w =Li-laurate Nastearatan Li-laurate (A)plus (B) :Rcpid 10,000 .do... 10,000 Q v10,000

.50% each in the mixture.

Example -I-V Sodium stearatewas added to lubricating oil 'A to make '20weight per cent soapin'the'o'il. This wasdiluted with octane-in theratio-ofone part soap-oil mixture to six parts of octane. The

Table II materials weremixedand passedmnder pressure. 40 through aheated section where the temperature mailman Bleeding was raised toabout-410 F. The liquid was disoomm -ram "Weight charged through anevacuated container andthe Strokes W vaporized octane removed. Theresidue was a mixture oflsoap'lumps and oil which on milling slow"; none42 313 13.3 DI dUC'Bd -21. grease of excellent quality. The no 3g 3 2'hardness o'f the finished grease can be increased r p by removingapart-of the-oil before milling or 4 Z H the hardness-decreased bythe-incorporati'onof Em-amp more oil. Severalother greaseswereprepared-using difo0 A EzmmpleV ferentsoap bases in con unction withdifferent oils; Penetration'testswere madeas in'Example Sodium stearatezw'as mixed with'oil *A and L-The efiect-of producing a grease by "ourheatedtoiabout 465F. The soap wasdispersed method is' clearly indicatedby data cont'ainedin in the oil to:-form.ailiquicl mixture. This mixturethex'ffilrgwing t 51 I was pouredintooil A which was :at about 250 TableHI Soap Penetration Content O Cooling Milling 'Penetraaiter 00,000 soapWeight iRate Strokes hon Additional per cent Strokes .kletrlrsteorate.20 A Slow none 202 Do 20 x ".00." 10,000 :151 202 1. 0" A LRapid 10,000 89 150 20 -]3 do. v10,000 133 100 20 0 do... 10,000 '102 100The-data in Table III show that an aluminum F. 'Thesoap solidified'to'atransparen't gel and stearate grease, which had been prepared'by 7nfloated in the-oil, in lumps. 'The "temperature methods employing slowcooling, had penetrations of 50, 151; and 202 in unworked, after beingworked 10,000 strokes, and after being worked 10 0;000 s'trokes,respectively. A grease similar in all resjpectsexcept2rapidly-cooled hada penetraafter mixing thetwo oilstogether'was about 285 F. The"excessoil'was drained oiiand the soap and a por'tionof theoilwas-worked severely to a grease which had a low loss jofcon'sistency-onextended working *and only a slight tendency to tiorrofimly 18$! at -1Gallic-strokes and -159at '100;000- bleed.

It may be desired to include some additives to give a finished greasecertain otherwise unobtainable desirable characteristics. Theseadditives may be added at any time during the process, but we prefer toadd them after the mixture has gelled and while the gel is being worked.In that manner the structure of the gel is not affected in itsformation.

In the past when hard soap cakes or lumps have appeared in the soap-oilmixture after heating and during the cooling step it has been thepractice to throw such mixtures away as it was believed they were notsuitable for th making of finished greases.

By the method of our invention we utilize such mixtures as those whichwere previously believed worthless, and gain from them a hard,even-textured, superior grease.

For those skilled in the art it will be obvious that many alterationsmay be made in the process of manufacture without change in theprinciple and the scope of our invention.

We claim:

1. A process for manufacturing a grease from an oil and a metallic soapwhich comprises the steps of forming a mixture comprising a metallicsoap with a hydrocarbon lubricating oil, heating said mixture withagitation to substantially disperse the soap in the oil, chillingsuddenly to form a hard friable gel in some free oil, separating saidgel from a portion of said free oil, and working said gel and remainingfree oil to a state of substantially constant consistency.

2. A process for manufacturing a grease from an oil and a metallic soapwhich comprises the steps of forming a mixture comprising said metallicsoap, containing substantially no free acid. with a hydrocarbonlubricating oil, heating to a temperature between about 365 F. and thedecomposition temperature of said mixture while agitating said mixtureduring said heating, chilling said mixture to form a hard fracturablegel in some free oil within from about seconds to about 300- seconds,separating said gel from a portion of said free oil, and working saidgel and remaining free oil to a smooth grease texture.

3. The process of claim 2 wherein said lubricating oil is substantiallysaturated with said metallic soap at a temperature within the hea ingrange specified. 1-

4. A process for manufacturing a grease from an oil and a metallic soapwhich comprises the steps of forming a mixture comprising said metallicsoap containing substantially no free acid, a hydrocarbon lubricatingoil and a low boiling diluent, heating said mixture to a temperaturebetween about 355 F. and about 540 F. while agitating said mixtureduring said heating, flash evaporating said diluent to form a hardfracturable gel residue in some free oil within from about 10- secondsto about 300 seconds, separating said gel from said free oil, andworking said gel to a smooth grease texture.

5. The process of claim 4, wherein said gel is separated from only aportion of said oil.

6. A process for manufacturing a grease from an oil and a metallic soapwhich comprises the steps of forming a mixture comprising said metallicsoap, containing substantially no free acid, and a hydrocarbonlubricating oil, heating said mixture to a. temperature between about365 F. and the decomposition temperature of said 10 mixture by means ofadding heated oil thereto while agitating, chilling said mixture to forma hard fracturable gel in some free oil within from about 10 seconds toabout 300 seconds, separating said gel from said free oil, and workingsaid gel to a state of substantially constant consistency.

7. A process for manufacturing a grease from an oil and a metallic soapwhich comprises the steps of forming a mixture comprising said metallicsoap, containing substantially no free acid, and a hydrocarbonlubricating oil, heating said mixture to a temperature between about 365F. and the decomposition temperature of said mixture by means of addingheated oil thereto while agitating, chilling said mixture to form a hardfriable gel in some free oil within from about 10 seconds to about 300seconds by means of suddenly mixing said mixture with a cold oil,separating said gel from a portion of said free oil. and working saidgel and oil to a smooth grease texture.

8. A process for manufacturing an improved grease from an oil and astifiening agent which stifiening agent is formed by the combination oflithium hydroxide and a fatty acid in the 010-014 range and in whichstiifening agent free acid has been substantially neutralized, whichprocess comprises the steps of forming a mixture of a hydrocarbonlubricating oil and said stiifening agent, mixing said mixture whileheating to a temperature between 365 F. and the decompositiontemperature of the ingredients so as to disperse the stiffening agent inthe oil, chilling said mixture to form a hard friable gel in some freeoil within from 1 second to about 600 seconds, and working said gel to astate of substantially constant consistency.

9. A process for manufacturing an improved grease from an oil and astifiening agent which stiffening agent is formed by the combination oflithium hydroxide and a fatty acid in the Clo-C14 range and in whichstiffening agent free acid has been substantially neutralized, whichprocess comprises the steps of forming a mixture of a hydrocarbonlubricating oil and said stifiening agent, mixing said mixture whileheating to a temperature between 365 F. and the decompositiontemperature of the ingredients so as to disperse the stiffening agent inthe oil, chilling said mixture to form a hard fracturable gel in somefree oil within from 10 seconds to about 300 seconds, and working saidgel to a smooth grease texture.

GRANT C. BAILEY. WILLIAM B. WHITNEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

tinuous Production of Grease, article in Industrial and Eng. Chem., vol.30, pp. 506 and 507, Apr. 1947.

1. A PROCESS FOR MANUFACTURING A GREASE FROM AN OIL AND A METALLIC SOAPWHICH COMPRISES THE STEPS OF FORMING A MIXTURE COMPRISING A METALLICSOAP WITH A HYDROCARBON LUBRICATING OIL, HEATING SAID MIXTURE WITHAGITATION TO SUBSTANTIALLY DISPERSE THE SOAP IN THE OIL, CHILLINGSUDDENLY TO FORM A HARD FRIABLE GEL IN SOME FREE OIL, SEPARATING SAIDGEL FROM A PORTION OF SAID FREE OIL, AND WORKING SAID GEL AND REMAININGFREE OIL TO A STATE OF SUBSTANTIALLY CONSTANT CONSISTENCY.